We knew Cities: Skylines was popular, but publisher Paradox Interactive confirmed it today, with a press release announcing that the game has sold over 2 million copies on Windows, Mac, and Linux PCs in the year since its release. It's the publisher's fastest-selling title ever.

The company plans to release a free update to the game for later this month.

The game broke one million sales within two months of its release, and has been boosted by mod support -- we spoke to developers Colossal Order about the program last year. We also have a close look at the design of the game's traffic system written by members of the development team. And if you're more of a video person, you can watch a postmortem of the game from GDC Europe, delivered by designer Karoliina Korppoo.

The 17-year old independent publisher behind the game, Paradox Interactive, recently laid plans to go public: "gaining access directly to the capital market gives great opportunities to make acquisitions like when we bought White Wolf in October 2015," CEO Fredrik Wester told Gamasutra.